In-plane compression performance of and integrated design/analysis tools for curvilinear steered fiber composites

Fiber placement enables production of complex composite structures in a cost-effective manner, and further enables structures exhibiting steered or curvilinear fiber paths. Steered fiber architecture may improve structural efficiency by tailoring local fiber orientation to the local internal load path.; This paper addresses management for a project team and techniques for material property evaluation of steered fiber structures. Nondestructive Evaluation (NDE) techniques and mechanical testing of steered fiber composite material are discussed. Reference geometry is one of the most important parameters in testing a steered fiber composite material. This is because local fiber orientation varies significantly unless coupons are positioned symmetrically about the centerline of a panel at the same radius. Macroscopic and microscopic methods for determining radius and centerline of available steered fiber composite panels are addressed.; This report identifies necessary mechanical compression tests to quantify the mechanical properties of steered fiber composites. Panels have been produced with continuously curvilinear fiber reinforcement, varying from less than 46 cm to more than 114 cm. Detailed mechanical tests are addressed in the following feature effect examinations: (1) Fiber steering radius variation, (2) Coupon width variation, (3) Coupon misalignment, (4) Minimum steering radius.; In the fiber steering radius investigation, test coupons were selected from radii of 58cm, 84cm and 109cm, and tested in compression to quantify the mechanical properties at each location. The coupon width variation testing is to assess suitability of standard test methods developed for linear composites to nonlinear steered composites. The tests were performed with 1.27cm, 2.54cm, and 3.81cm specimen widths. The misalignment effect in composite structure was investigated with 0°, 5° and 10° misalignment of the coupon with respect to the tangent of the fiber steering axis. For the minimum steering radius investigation, specimens obtained from 58cm, 84cm and 109cm radii were used to compare and to verify the difference of mechanical properties between the locations.; Theoretical analyses were performed with same feature investigations. The results show the misalignment of test coupon is a dominant factor in mechanical performance. Fiber steering and specimen width variation found to be minor effects in mechanical properties.; Mechanical test data compare favorably to theoretical analyses. Although there is a theoretical change in mechanical properties with fiber steering radius, in practice the effect is much less sensitive than that due to misalignment of the test coupon. Expected additional reduction in mechanical performance at tighter steering radii due to increased levels of observed tow buckling are not observed even the theoretical model did not account the tow buckling. As such it appears that steering radii of 58cm produce acceptable quality specimens, and thus the minimum allowable steering radius must be less than this.